This invention relates to a sequencing die and method for forming truss webs or links from metal tubing.
Composite truss joists comprising spaced, elongate wood chords interengaged by metal webbing, such as shown in my prior U.S. Pat. No. 3,137,899, have become widely used in many types of structural applications. The webs used in these trusses generally are formed from metal tubing and comprise a medial tubular portion with flattened web ends at each extremity defining a central cross pin receiving hole.
Heretofore, the apparatus for forming these webs have formed webs with margins between the flattened web ends and the medial portions of the webs which are substantially normal to the longitudinal axes of the webs. Thus when the webs are positioned between the chords, portions of the flattened web ends necessarily are unsupported by the chords. These unsupported portions are subject to easy bending when compressive forces are transmitted through the webs. To overcome this weakness prior art webs have formed from tubing that was larger than otherwise required, thus increasing the weight and cost of the truss.
In addition the prior web forming apparatus have not flattened the web ends completely before initiating punching of the cross pin receiving holes and shearing of the terminal portions. Thus the web ends are never completely flattened due to interference from the punch. Conversely the web ends interfere with the punch causing difficulty in stripping the punch and increased punch wear. This also causes the holes to be formed slightly elliptical with jagged edges and not centered accurately laterally in the web ends, nor located accurately relative to their terminal portions. Therefore, the cross pins do not fit tightly in their holes, resulting in wear of the pins and causing dimensionally inaccurate trusses.
Furthermore, the prior web forming apparatus flatten the web ends while supporting the medial portions of the webs rigidly, thus causing the web ends to be laterally displaced and thus offset from the longitudinal center line of the webs.
Accordingly, it is the principal object of the present invention to provide a sequencing die for forming truss joist webs which flattens the web ends completely before initiating punching of the crosspin receiving holes and trimming their terminal portions.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having means to form diagonal chard-supporting margins between the web ends and the medial portions of the webs.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having means to form opposed triangular semiflattened portions on both sides of the web ends adjacent the margins between the web ends and the medial portions of the webs.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having gripping means configured to support the webs during flattening of the webs in a manner allowing gradual lateral displacement of the webs proportional to the amount of flattening, thus forming web ends which are aligned with the longitudinal center line of the webs.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having indexing means to index the webs longitudinally relative to the die assembly to form dimensionally accurate web lengths.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having antitwisting means associated with the indexing means to allow indexing the webs during forming in a manner giving angularly aligned web ends.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs of different diameters and wall thicknesses.
It is a further object of the present invention to provide a sequencing die for forming truss joist webs having means to punch cross pin receiving holes of different diameters in the web ends of different webs, or in opposed web ends of the same web.